Analogous Atomic and Electronic Properties between V N and V N C B Defects in Hexagonal Boron Nitride

We investigate defect properties in hexagonal boron nitride (hBN) which is attracting much attention as a single photon emitter. Using first-principles calculations, we find that nitrogen-vacancy defect V N has a lower energy structure in C 1 h symmetry in 1− charge state than the previously known D 3 h symmetry structure. Noting that carbon has one more valence electron than boron species, our finding naturally points to the correspondence between V N and V N C B defects with one charge state difference between them, which is indeed confirmed by the similarity of atomic symmetries, density of states, and excitation energies. Since V N C B is considered as a promising candidate for the source of single photon emission, our study suggests V N as another important candidate worth attention, with its simpler form without the incorporation of foreign elements into the host material.

We Are Never Ever Getting (back to) Ideal Symmetry: Structure and Luminescence in a Ten-Coordinated Europium(III) Sulfate Crystal

Our theoretical treatment of electronic structure in coordination complexes often rests on assumptions of symmetry. Experiments rarely provide fully symmetric systems to study. In solution, fluctuation in solvation, variations in conformation, and even changes in constitution occur and complicates the picture. In crystals, lattice distortion, energy transfer, and phonon quenching is in play, but we are able to have distinct symmetries. Yet the question remains: How is the real symmetry in a crystal compared to ideal symmetries? Moreover, at what level of detail do we need to study a system to determine, if the electronic structure behaves as if it has ideal symmetry? Here, we have revisited the Continues Shape Measurement (CShM) approach developed by Ruiz-Martínez and Alvarez to evaluate the structure of ten-coordinated europium(III) ions in a K5Na[Eu2(SO4)6] structure. By comparing the result of the symmetry deviation analysis to luminescence data, we are able to show the effect of small deviations from ideal symmetry. We suggest using a symmetry deviation value, σideal, determined by using our updated approach to Continues Shape Measurements, where we also align the structure via our AlignIt code. AlignIt includes normalization and relative orientation in the symmetry comparison, and by combining the calculated values with the experimentally determined energy level splitting, we were able create the first point on a scale that can show how close to ideal an experimental structure actually is.

Sym3DNet: Symmetric 3D Prior Network for Single-View 3D Reconstruction

The three-dimensional (3D) symmetry shape plays a critical role in the reconstruction and recognition of 3D objects under occlusion or partial viewpoint observation. Symmetry structure prior is particularly useful in recovering missing or unseen parts of an object. In this work, we propose Sym3DNet for single-view 3D reconstruction, which employs a three-dimensional reflection symmetry structure prior of an object. More specifically, Sym3DNet includes 2D-to-3D encoder-decoder networks followed by a symmetry fusion step and multi-level perceptual loss. The symmetry fusion step builds flipped and overlapped 3D shapes that are fed to a 3D shape encoder to calculate the multi-level perceptual loss. Perceptual loss calculated in different feature spaces counts on not only voxel-wise shape symmetry but also on the overall global symmetry shape of an object. Experimental evaluations are conducted on both large-scale synthetic 3D data (ShapeNet) and real-world 3D data (Pix3D). The proposed method outperforms state-of-the-art approaches in terms of efficiency and accuracy on both synthetic and real-world datasets. To demonstrate the generalization ability of our approach, we conduct an experiment with unseen category samples of ShapeNet, exhibiting promising reconstruction results as well.

Simulation Study of In-Phase and Out-Phase Enhanced Absorption of Graphene Based on Parity–Time Symmetry One-Dimensional Photonic Crystal Structure

In the field of modern optical communication systems and photoelectric detection, new components with complex functions and excellent performance are urgently needed. In this paper, a graphene-based parity–time (PT) symmetry structure is proposed, which is achieved by preparing the graphene layer on the top of a PT-symmetry photonic crystal. The transfer matrix method was used to calculate the absorptance of graphene, and a unique amplified absorption effect was found. Meanwhile, the peak value and wavelength position of the absorption can be modulated via the applied electric field. The results show that by adjusting the negative square-wave electric field from −3.5 × 10−5 to −13.5 × 10−5 V/nm (or the positive square-wave electric field from 2 × 10−5 to 11 × 10−5 V/nm), the proposed structure can achieve in-phase (or out-phase) enhanced absorption for the communication wavelength 1550 nm, with the absorption of graphene from 17 to 28 dB (or 30 to 15 dB) corresponding to the square-wave modulation electric field change. The modulable absorption properties of graphene in the structure have potential in optoelectronic devices and optical communication systems.

Proper time reparametrization in cosmology: Möbius symmetry and Kodama charges

It has been noticed that for a large class of cosmological models, the gauge fixing of the time-reparametrization invariance does not completely fix the clock. Instead, the system enjoys a surprising residual Noether symmetry under a Möbius reparametrization of the proper time, which maps gauge-inequivalent solutions to the Friedmann equations onto each other. In this work, we provide a unified treatment of this hidden conformal symmetry and its realization in the homogeneous and isotropic sector of the Einstein-Scalar-Λ system. We consider the flat Friedmann-Robertson-Walker (FRW) model, the (A)dS cosmology and provide a first treatment of the model with spatial constant curvature. We derive the general condition relating the choice of proper time and the conformal weight of the scale factor, and give a detailed analysis of the conserved Noether charges generating this physical symmetry. Our approach allows us to identify new realizations of this symmetry while recovering previous results in a unified manner. We also present the general mapping onto the conformal particle and discuss the solution-generating nature of the transformations beyond the Möbius symmetry. Finally, we show that, at least in a restricted context, this hidden conformal symmetry is intimately related to the Kodama charges of spherically symmetric gravity. This new connection suggests that the Möbius invariance of cosmology is only the corner of a larger symmetry structure which could be relevant beyond cosmological models.

Knot Semantic Logic and Deep Structure of Statements

This article aims to analyze the deep structure of sentences by applying the knot semantic logic principle in the surface structure of the sentences. This article will help to judge some controversial statements that have legal and social effects. The knot semantic logic theory is a novel approach to explaining a literature’s symmetry structure. Chiasm, parallelism, and concentricity are all examples of symmetry structure. This new theory introduces a new method for detecting symmetry in words, sentences, verses, essays, chapters, and entire books. This analysis will use Knot semantic logic point of view. The methodology used in the analysis has two main procedures: (1) classification of the structure and (2) analyzing some examples from some official/formal statements and controversial statements using Paltridge’s classification of thematic progression and knot semantic logic. The result of this research is that the valid argument has surface and Deep Structure. Some fallacies statements such as presumption, generalization, distortion, and deletion have a deep structure that forms ring composition (Type I of knots semantic logic) and parallelizations (Type III of knots semantic logic). This research results generate a new idea about perspective truth, Original perspective domain, and Response perspective domain

Simulation Research on Blood Detection Sensing with Parity-Time Symmetry Structure

To realize the design of a medical sensor with excellent comprehensive performance indexes, herein, a plasma concentration sensing model satisfying the Parity-Time (PT) symmetric condition is proposed. In this paper, the transfer matrix method was used to simulate the transmittance spectrum of the structure, according to the amplification effect on defect mode transmission and various detection performance indexes of the structure. We numerically optimized the parameters of the structure, such as the number of PT-symmetry unit cell N, the sample layer thickness dD as well as the macroscopic Lorentz oscillation intensity α in the PT-symmetry unit cell. The calculation results demonstrate that when the sample concentration changes from 0 g/L to 50 g/L, the wavelength of defect peak shifts from 1538 nm to 1561 nm, and the average quality factor, sensitivity, average figure of merit, average detection limit and average resolution of the structure can reach 78,564, 0.4409 nm/(g/L) (or 227.05 nm/RIU), 11,515 RIU−1, 5.1 × 10−6 RIU and 0.038 g/L, respectively. Not only the sensitivity and resolution of the PT-symmetry structure are better than that of the similar sensors, but it also has excellent comprehensive detection performance, which indicates that the developed sensor can be used in high-precision biomedical detection devices.

Active Disturbance Rejection Control of Underwater Vehicle with Omnidirectional Control

This paper focuses on the omnidirectional drive characteristics and autonomous control of the underwater saucer glider under the condition of underactuated and multiconstraints. Firstly, the dynamic model of the underwater saucer glider is established, and the underactuated control characteristics and the plane biaxial symmetry structure characteristics of the underwater saucer glider are analyzed. An omnidirectional drive mechanism with four water jet thrusters is designed, and the omnidirectional control power output equation is given. Secondly, a nonlinear active disturbance rejection controller is designed, and a visual simulation platform of UUVs based on MATLAB + MFC is established. Through a large number of numerical tests, the reliability and effectiveness of the control strategy are verified, and the smooth operation of the underwater saucer glider in the dynamic process of three-dimensional space is realized.